1. Field of the Invention
This invention relates to an acoustic device, specifically one for being installed in a vehicle.
2. Background Art
The interior configuration of a vehicle is quite complicated and it imposes restrictions on the arrangement of speakers within its interior. The sound pressure level of the acoustic power generated by a speaker and the sound quality consequently vary with the position where a listener is seated. FIG. 1 shows an example of the arrangement of front speakers 1 and rear speakers 2. In order to minimize the problem of sound variation within the vehicle, the audio signal output of an amplifier 3 is, as shown in FIG. 2, supplied to the front and rear speakers 1 and 2 connected in series thereto through a so-called power feeder 4 which divides its output in a conventional vehicular acoustic device. The power feeder 4 is formed with a circuit having two variable resistors 41 and 42 connected in series and the circuit is connected to the outputs of the amplifier 3 at one end and to both ends of the series speaker circuit consisting of the speakers 1 and 2 at the other. For a stereo speaker system, there are two such series circuits with respective ganged power feeders 4. Moreover, the contact points between the variable resistors 41 and 42 are connected to the contact points between the speakers 1 and 2.
The acoustic power levels of the speakers 1 and 2 are each adjusted by adequately setting the resistances of the variable resistors 41 and 42 thus arranged and the desired sound pressure level is set in a fixed listening position. However, it is troublesome to make such adjustment according to the listening position and changes in sound quality resulting from changes in the listening position have not properly been dealt with.